This invention relates to an improved control for an electric assist vehicle and more particularly to an improved control that will ensure against electric driving of the vehicle in the event of abnormal conditions.
It has been proposed to provide a manually powered vehicle with an electric assist so as to assist the occupant in the manual propulsion of the vehicle. For example, the copending application of Nozomu Takata, Ser. No. 08/059,540, filed May 10, 1993 and entitled "Bicycle with Electric Motor," now U.S. Pat. No. 5,370,200, issued Dec. 6, 1994, and assigned to the assignee hereof, shows a manually powered vehicle such as a bicycle wherein there is provided an electric power assist for assisting the occupant in the powering of the vehicle. This type of mechanism includes an arrangement that senses the manual input force or torque exerted by the occupant and then powers an electric motor by connecting it to a battery in such a way so as to provide a degree of assist in proportion to the manual input force.
This type of vehicle has a large number of advantages. However, it is important to ensure that the amount of electrical power supplied to the electric motor cannot be too great under certain circumstances so as to permit the speed of the vehicle to become excessive. In addition, it should be ensured that the system will not permit the operator to bypass the control and operate the electric motor manually which might also result in excessive speed of the vehicle. The aforenoted copending application discloses a number of ways in which these effects can be obtained.
In all of the systems disclosed in the aforenoted copending application, the control senses only abnormal variations in the force sensed and provides safety disconnect of the electric motor power in the event the force sensor becomes inoperative or is bypassed. Although this has a number of advantages, further improvements or alternative constructions may be desirable.
It is, therefore, a principal object of this invention to provide an improved electrically assisted vehicle that has safety features.
It is a further object of this invention to provide an improved electrically assisted vehicle wherein both the speed and the input force are compared so as to determine when an abnormal condition exists.